Seedless watermelon (Citrullus lanatus (Thunb.) Matsum. And Nak.) production involves using pollen from diploid male parent plants to fertilize flowers of tetraploid (2n=4x=44) maternal parent plants. Pollination of the tetraploid flowers with diploid pollen leads to hybrid F1 seeds which are triploid (Kihara, 1951, Proceedings of American Society for Horticultural Science 58: 217-230; Eigsti 1971, Hort Science 6: 1-2). The triploid hybrid plants, grown from these F1 seeds, are self-infertile as they produce sterile pollen due to chromosome imbalance (Fehr, 1987). The triploid hybrids, therefore, need to be pollinated by a diploid pollenizer to produce watermelon fruit. Triploid plants are, therefore, interplanted with pollenizer plants for fruit production. The “seedless” fruit produced after pollination on the triploid hybrid plant are often not truly seedless, but may contain some undeveloped, small, pale seeds, which are edible.
For optimal seedless watermelon fruit set, sufficient viable pollen is required. Plants are generally planted at a ratio of 1 pollenizer per every 2-4 triploid plants. Triploid plants and pollenizers are either planted in separate rows (e.g. 1 row of pollenizer and 2-4 rows of triploids), or interplanted within rows (e.g. planting 1 pollenizer plant in between 2 to 3 triploid plants in the same row), or interplanted in narrow rows between rows of triploids (see US 2006/0168701 Table 2). The fruit produced on the pollenizer plants preferably has a different rind pattern from the fruit on the triploid hybrids, so that these can be easily distinguished. Until now, generally the fruits produced on dedicated pollenizer plants are not harvested or discarded and only the seedless triploid fruits are sold.
In the last years, several dedicated pollenizer plants have been developed, which provide sufficient staminate flowers and sufficient viable pollen throughout the season to increase triploid fruit yield. These dedicated pollenizers include for example varieties Polimax and Jenny (Nunhems), Sidekick (Harris Morin), Companion (Seminis) and the Super-Pollenizers SP-1 and SP-4 (Syngenta). These dedicated pollenizers can be divided into two categories based on their vegetative growth type, which is either of the standard vine length e.g. Jenny and SP-1 and SP-4, or the ‘compact’ vine length, e.g. Companion or Sidekick.
Some pollenizers produce diploid fruits which could be marketable, while others produce fruits that are unsuitable for consumption and marketing. Dittmar (2006, MSc Thesis North Carolina State University, Horticultural Science, Characterization of diploid watermelon pollenizers and utilization for optimal triploid watermelon production and effects of halosulfuron post and post-dir on watermelon) evaluated different pollenizers for the potential marketability of their fruits and concluded that Mickeylee, SF800, MiniPool, Jenny and Pinnacle have a fruit quality that could potentially be marketed. Average fruit weight of these was 5.1 kg, 10.7 kg, 3.9 kg, 3.3 kg and 2.9 kg respectively (Dittmar 2006, supra). The smallest diploid fruits were produced by Sidekick (1.0 kg, with dimensions of 12.3×11.9 cm length:width Dittmar 2006, supra) and SP-1 (2.0 kg, with dimensions of 17.5×15.4 cm length:width (Dittmar 2006, supra), but neither of these produce marketable fruits. The fruits of Sidekick are very poor quality pink-fleshed and those of SP-1 are white-fleshed and have a low brix value. Due to the non-marketable fruits, these pollenizers are referred to as being “non-harvestable pollenizers”.
US2009/0288183 (Gold Seed Co. LLC) describe a pollinizer called “Escort-4” which produces small fruits having reduced sugar for type 2 diabetics, referred to as a “dual purpose reduced sugar watermelon”. The fruits are said to have an average weight of 4.0 lbs (1.8 kg) and a size of 5-7 inches long (12.7-17.7 cm)×4-5 inches wide (10.1-12.7 cm). The fruits of Escort-4 are said to have approximately ⅓ less sugar content than commercial diploid varieties, such as Sangria (Syngenta Inc.).